Idle speed control systems are known which control engine idle speed by both ignition timing control and control of a bypass throttle valve. When the idle speed control mode is first entered, an initial bypass throttle position is generated as a function of predetermined conditions such as air conditioner status. This initial or open loop value is then adjusted by a feedback signal derived from a difference between desired engine speed and actual engine speed. Ignition timing is also adjusted by the feedback signal to provide faster corrections than obtainable by bypass throttle control alone. Such a control system is disclosed in U.S. Pat. No. 5,303,168.
Engine control systems are also known which retard ignition timing during cold operation to more rapidly warm the catalytic converter. Such a system is disclosed in U.S. Pat. No. 4,144,853.
The inventors herein have recognized numerous problems with the above approaches. One such problem is that the retard in ignition timing for rapid converter heating, may also cause a decrease in desired idle speed provided by the initial throttle position. Stated another way, the inventors herein have recognized that the initial throttle position requires correction for the retarded ignition timing provided to rapidly heat the converter.